Technical Session XV (Saturday, November 2, 2013, 9:45 AM) which is situated on the eastern Bolivian Altiplano (21° 52’ S, 66° 19’ W), several THE SIRENIAN GENUS METAXYTHERIUM: WHAT'S UP WITH THOSE kilometers southeast of the village of Cerdas (approx. 60 km southeast of Uyuni). Eight ANIMALS?? specimens were studied including several partial mandibles preserving posterior premolars and molars, a partial maxilla with P3-P4, two fragmentary dentaries preserving DOMNING, Daryl, Howard Univ., Washington, DC, United States, 20059; VELEZ- alveoli of the anterior dentition, several isolated cheek teeth, an upper incisor, and two JUARBE, Jorge, Florida Museum of Natural History, Gainesville, FL, United States calcanei. The specimens are referred to the Hegetotheriinae based on the absence of a Metaxytherium (Mammalia, Dugongidae) is one of the most widespread, long-lived, strongly trilobed m3 talonid, lack of conspicuous diastemata among i2-p2 alveoli, and a species-rich, commonly fossilized – and taxonomically troublesome – genera of Sirenia. relatively small I1. A Hegetotheriine affinity is supported by the two Cerdas calcanei, Its morphologically conservative nature had, until recently, made it difficult to properly which are more similar to Hegetotherium than Pachyrukhos in having a circular define this genus. In recent years, however, much has been done to clarify its contents, sustentacular facet, a large navicular facet, and an only moderately rugose tuber. The relationships, and eventful evolutionary history. Originally known only from the Miocene Cerdas species differs from Prohegetotherium in lacking a labial groove near the anterior and Pliocene, its presence in the New World late Oligocene is now established, along margin of the upper cheek teeth. The p3 of the Cerdas species differs from that of with that of a new, early Oligocene genus likely ancestral to it. An apparently anagenetic Sallatherium in having the trigonid shorter than the talonid; the opposite is true in lineage of West Atlantic-East Pacific species persisted into the late Miocene. A parallel Sallatherium. It differs from Hemihegetotherium in having upper and lower cheek teeth European-Mediterranean lineage may also have begun in the late Oligocene, and ended with flat rather than convex lingual faces and in having a more rounded molar trigonid. only in the mid-Pliocene. Both showed a tendency towards increasing body size. The Cerdas species is conservatively referred to the genus Hegetotherium based on its However, the zoogeographic connections between these lineages are unclear, and the generally rectangular upper cheek teeth and semi-elliptical talonids. However, the lack of early to late Miocene members of both lineages exhibit near-stasis in morphology – a shallow buccal groove on the m3 talonid suggests it may pertain to a distinct genus. A something not seen elsewhere in the Sirenia. The latest Miocene and Pliocene phylogenetic analysis testing this proposition is in progress. Linear measurements of the Mediterranean species, in contrast, display relatively rapid evolution, along with Cerdas specimens are 20–30% smaller than those of other hegetotheriines and fall outside ecophenotypic dwarfing during the Messinian Salinity Crisis. A long-standing puzzle, the the range of variation of 120 Hegetotherium mirabile specimens from Santa Cruz, mid-Miocene (Badenian) “M. petersi” from the Vienna Basin, seems to be at most a Argentina. Thus, it clearly represents a distinct species. The absence of pachyrukhines peripheral variant of the western European type species M. medium. At the opposite, East from early and middle Miocene faunas of northern Chile and Bolivia suggests that small Pacific end of the genus’ range, M. arctodites is the sister group and structural ancestor of hegetotheriines such as the new Cerdas species may have occupied a pachyrukhine-like the Hydrodamalinae (Dusisiren + Hydrodamalis), rendering the halitheriine genus ecological niche in the middle latitudes of South America during this interval. Metaxytherium paraphyletic. For the most part, these tropical marine herbivores may have owed their success to being ecological generalists that fed on seagrass leaves and the rhizomes of the smaller Romer Prize Session (Thursday, October 31, 2013, 8:45 AM) seagrass species. For most of their history, they coexisted with more diverse and QUANTIFYING PERIODS OF DIFFUSION IN MARINE AND TERRESTRIAL morphologically flamboyant but more specialized and shorter-lived species of MAMMALIAN VERTEBRATE FOSSILS USING RARE EARTH ELEMENTS Dugonginae, which evidently ate larger and tougher rhizomes. Notably conservative in retaining small tusks through most of the Miocene, Metaxytherium then diversified DREWICZ, Amanda, Boise State University, Boise, ID, United States, 83702 surprisingly, in opposite directions: losing tusks altogether as they evolved into Rare earth (REE), trace elements (TE) and isotopes in vertebrate fossils have been hydrodamalines in the Pacific, but growing much larger, dugongine-like tusks in the used to study taphonomy/reworking, stratigraphic correlation, paleoenvironment Mediterranean species M. serresii and M. subapenninum. Clearly, past evolutionary reconstruction and fossilization processes. REE/TE/isotopes diffuse into bone during performance is no guarantee of future results! fossilization. The period of diffusion limits the temporal resolution of paleoenvironmental interpretations made from REE/TE/isotopes. Periods of incorporation have been calculated in only a few studies and additional measurements will better refine Technical Session II (Wednesday, October 30, 2013, 8:15 AM) temporal resolution of geochemically based paleoenvironmental reconstructions. Five Late Eocene brontothere bones from the White River Group and four Miocene marine WAS THE GIANT SHORT-FACED BEAR ARCTODUS SIMUS A HYPER- mammals from the Atlantic Coastal Plain were analyzed for REE/TE concentrations SCAVENGER? A NEW APPROACH TO THE DIETARY STUDY OF URSIDS using Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Of the five USING DENTAL MICROWEAR TEXTURES brontothere bones, four were from the same bonebed. An outer circumferential layer (OCL) was preserved on the margin in two brontothere bones and had lower DONOHUE, Shelly, Vanderbilt University, Nashville, TN, United States, 37235; concentrations than underlying bone, suggesting a lack of REE/TE incorporation into the DESANTIS, Larisa, Vanderbilt University, Nashville, TN, United States; SCHUBERT, OCL or subsequent leaching. Elevated concentrations were noted surrounding some Blaine, East Tennessee State University, Johnson City, TN, United States; UNGAR, osteon channels, indicating that Haversian systems may act as fluid conduits, bringing Peter, University of Arkansas, Fayetteville, AR, United States unreacted fluid into bone. REE depth fractionation tends to be less pronounced in marine The Pleistocene short-faced bear, Arctodus simus was the largest member of the bones (when compared to terrestrial bones) which may result from a greater influence of order Carnivora to traverse North America, yet whether this giant was primarily an active secondary diffusion pathways (Haversian systems). Diffusion periods for six REE were predator, opportunistic omnivore, or bone crushing hyper-scavenger remains unknown. internally consistent and ranged from 0.9+/-0.2 to 2.8+/-0.6 ka in marine bones and Dental microwear has the potential to offer new insight into this debate. Here, we 2.2+/-0.5 to 54.8+/-1.5 ka for terrestrial bones. Faster diffusion periods within marine investigate the application of dental microwear texture analysis to bears through bones suggest that fossilization occurs over a shorter timespan in saturated environments. compiling a baseline that correlates microwear attributes of lower first and second molars Diffusion periods differed in brontothere bones from a single bonebed, which has (m1 and m2, respectively) to known feeding behavior in modern bears. Resulting implications for the fidelity of bulk sample analyses regarding temporal resolution of baseline data is then used to evaluate the hypothesis that Ar. simus was a bone consuming REE/TE/isotopes in paleoenvironmental reconstructions. Previous studies have reported hyper-scavenger at Rancho La Brea, California. Results of texture analysis evince soft tissue preservation within fossil bone and concluded that the rate of diffusion must significant variation along the tooth row, with the crushing/grinding functionality of the have outpaced the rate of decay in order to preserve soft tissue. Rates of REE/TE m2 serving as a better dietary recorder than the slicing/shearing m1 carnassial. Texture diffusion suggest that biomolecule preservation in deep time would be favored in analysis of the m2 shows significant variation among extant species that correlates with saturated environments (marine, lacustrine, channel). physical properties of known diets. Microwear complexity (Asfc) is significantly higher, and more variable for carnivorous and omnivorous ursids (Ursus maritimus, mean Asfc = 8.49; U. americanus, mean Asfc = 7.85) in comparison to more herbivorous bears (Ailuropoda melanoleuca, mean Asfc = 1.996; Tremarctos ornatus, mean Asfc = 4.172; Symposium 4 (Saturday, November 2, 2013, 10:30 AM) U. malayanus, mean Asfc = 3.96). High anisotropy (epLsar) further differentiates A. EVIDENCE FOR A DISTINCT EARLY MAASTRICHTIAN POLAR DINOSAUR melanoleuca (epLsar = 0.0039) from U. maritimus (epLsar = 0.0022) and U. americanus FAUNA